Indirect printing methods generally include a two-step printing process involving first applying ink imagewise onto an intermediate transfer member (such as a drum or a belt) using an inkjet printhead to form a transient image, and then transferring the transient image to a substrate. When the ink is applied onto the intermediate transfer member (also called, for example, an intermediate receiving member, a blanket, or a transfix blanket), it wets or spreads to form a transient image. The transient image then undergoes a change in properties (such as partial or complete drying, thermal or photo-curing, gelation, and so forth), and is transferred to the substrate. An exemplary offset or indirect printing process is disclosed in U.S. Pat. No. 5,389,958, the disclosure of which is incorporated herein by reference.
Intermediate transfer members suitable for use in indirect printing desirably exhibit surface properties (such as energy, topology, and so forth) that meet the sub-system requirements of the inkjet/transfix printing architecture, including wetting of the ink and subsequently (such as after phase change or the like) transferring the transient image (that is, the residual ink film along with pigment) onto a substrate. Several classes of materials may be used to form intermediate transfer members, including silicone, fluorosilicone, and Viton. However, these are hydrophobic materials, and the inherent low surface tension of these materials precludes wetting of aqueous ink drops. A higher surface tension material may be used to form the intermediate transfer member, but the high surface tension of such materials would impede efficient transfer of the image from the intermediate transfer member.
Because the surface free energy requirements of the intermediate transfer member desirable for wetting the ink are different than those for transferring the transient image, intermediate transfer members that display good wettability do not efficiently transfer the ink film onto a substrate, and conversely, intermediate transfer members that efficiently transfer the image to the substrate do not wet the ink. Thus, to date, intermediate transfer members have not enabled both functions (that is, both wetting and transfer).